/Engine/Source/Developer/ScreenShotComparisonTools/Public/ImageComparer.h
https://en.wikipedia.org/wiki/Structural_similarity
double CompareStructuralSimilarity ( const [FComparableImage](API\Developer\ScreenShotComparisonTools\FComparableImage) * ImageA, const [FComparableImage](API\Developer\ScreenShotComparisonTools\FComparableImage) * ImageB, [EStructuralSimilarityComponent](API\Developer\ScreenShotComparisonTools\FImageComparer\EStructuralSimil-) InCompareComponent, const [FString](API\Runtime\Core\Containers\FString) & OutDeltaPath )